Alcan diecasting process to be licensed in North America. (New Process).

The search for production efficiency often leads to innovative technology. That was the case when Alcan Automotive (Alcan, Inc.), headquartered in the U.S. in Farmington Hills, Michigan, was challenged by Audi to develop several thin-walled, large-surface castings for a mass-produced automotive use. Alcan Automotive responded by using its High-Q-Cast technology to produce assembly-ready castings at its Alcan BDW GmbH & Co. KG plant, Markt Schwaben, Germany.

Initially developed and patented by Alcan in 1996, this casting technology is a cold chamber diecasting process that produces premium aluminum and magnesium castings with laser and MIG weldability, excellent mechanical properties and high flow length: wall thickness ratios. Used by Alcan for a variety of automotive applications in Europe, the company is now seeking to license the technology to a select number of diecasters in North America.

"We were already working with Audi on some aluminum castings when the auto manufacturer approached us about developing all of the structural castings, including the B-pillar for the A2--a much smaller, but higher volume car sold in Europe," said Martin Hartlieb, sales director--engineered shaped products for Alcan Automotive. "We worked closely with members of Audi's development team for more than two years to complete the process before the car went into production at their Neckarsulm facility in Germany."

Besides requiring a thin-walled part that could be welded during production, Audi needed a B-pillar that would be crashworthy, have minimum distortion, and improve production and cost efficiencies.

Alcan met the criteria by creating a 4-ft tall casting that replaced eight separate stampings yet weighs only 5 lb. The casting included mounts for door hinge reinforcements and seat belt height adjustment, while meeting the requirements for side-impact collisions, Dimensional tolerances were held to [+ or -] 0.2 to 1 mm.

The High-Q-Cast casting technique is based on Alcan's minimum fill time (MFT) technology, but is a more comprehensive process that includes characteristics such as a special heat treatment (when needed), precise lubrication, process control within a small window, extensive process simulation, unique gating design and the use of degassing equipment. The MFT technology employs vacuum evacuation of the die, as well as a specialized feed system and gating design.

A critical component of the MFT technology is an integral process monitoring and real-time shot control system. Since 1994, Alcan has used SureTrak digital control systems supplied by Visi-Trak Worldwide, LLC, Valley View, Ohio. The SureTrak controls monitor a number of functions, including impact pressure, feeding stroke, slow shot velocity, fast shot velocity, vacuum pressure and time, temperature heating circuits, smelt temperature and humidity inside the die cavity.

The process control system also helped Alcan achieve the mechanical properties required for the Audi B-pillar by eliminating oxides, inclusions and porosity during casting. Other factors contributing to the mechanical properties were tooling design to avoid turbulent metal filling and quenching, and temperature and annealing time adapted specifically to the AURAL-2 alloy.

Maintaining the tight dimensional tolerances required several steps during the casting and cooling of the pillar. The process begins with a die design incorporating supports that enable the part to be removed without deformation. Before casting, a robot applies casting lubricant on critical areas of the die to ensure easy removal.

Once the part is removed, it is slowly cooled with a special water shower. A shock-free transport system then carries the part to heat treatment. Heat treatment is done at a lower temperature with air quenching to keep the tolerances consistent throughout the process.

The selective application of casting lubricant and cooling water also contributes to casting a part that is suitable for MIG and laser welding. Other attributes of the High-Q-Cast technology also play a role in weldability. The tool design ensures that the die metal filling and solidification are homogeneous, while the treatment of the melt prevents gas in the alloy.

"We learned several important lessons in producing the B-pillar for the Audi A2," said Hartlieb. "Simultaneous engineering is essential in material selection, process development, and part and die design. Also, it is absolutely necessary to coordinate with all partners for supply chain management."

Select No. 018 at www.moderncasting.com/into